Designing properties of (Na_1/2Bi_x)TiO₃-based materials through A-site non-stoichiometry

Abstract

Modification of microstructure and electrical properties due to high A-site diffusion of cations induced by non-stoichiometry during processing.

Enabling nanoscale flexoelectricity at extreme temperature by tuning cation diffusion

“…According to our recent work 21 , this stoichiometry should lead to a much more homogeneous Sr 2+ distribution within the nanoparticle rendering no core–shell structure and thus no noticeable strain gradient. The experimental setup and working environment were identical.…”

“…First, NBT-25ST has a high dielectric constant, which gives rise to a high flexocoupling coefficient. Second, the Sr 2+ diffusion can be accelerated or suppressed dramatically by modifying the A-site stoichiometry 21 . This renders an attractive system to tune cation diffusion and to generate a strain gradient without additional mechanical loading.…”

“…This is a direct consequence of the slow diffusion of the Sr 2+ in stoichiometric NBT-25ST 8 . A gradient of Sr 2+ leads to a chemically induced lattice strain because of the differences in ionic radii of the A-site cations 21 . This effect is usually referred as the Vegard effect 29,30 .…”

“…In our case, the oxygen vacancies may similarly influence the strain distribution and therefore the polarization by the flexoelectric effect. However, the resistivity of NBT-25BT bulk samples is relatively high even at 800 °C 21 and it was not possible to measure the standard semi-circles expected in Nyquist plots. In situ TEM measurements to quantify the role of oxygen vacancies on flexoelectricity with atomic resolution at 800 °C falls out of the scope of the present article.…”

“…Previous studies 19–21 showed that compositional gradients can be obtained by utilizing the diffusion of strontium cations in bulk ceramics and nanoparticles of 0.75 sodium bismuth titanate −0.25 strontium titanate (NBT-25ST). By making use of this compositional gradient, a strain inhomogenity and therefore, a flexoelectric-based polarization can be induced.…”